The present invention relates to a novel process for overcoating multicoat color and/or effect paint systems comprising at least one color and/or effect basecoat (A) produced from at least one aqueous basecoat material (A) and at least one clearcoat (B) produced from at least one liquid clearcoat material (B). The present invention relates in particular to a novel process for overcoating, on the line at the automaker's plant, damaged or undamaged multicoat color and/or effect paint systems produced by means of electrostatic spray application (ESTA).
In the overcoating of multicoat color and/or effect paint systems on motor vehicles, especially automobiles, with refinishes there are often shifts in shade and/or changes in the optical effect, especially the metallic effect. In many cases the cause of these unwanted changes is the fact that the multicoat paint systems, also referred to by those in the art as original finishes or OEM finishes, are applied by means of electrostatic spray application (ESTA) whereas the refinishes are applied pneumatically. The different application methods lead in fact to a difference in the orientation of the color and/or effect pigments in the resultant basecoats.
The basic assumption in the art is that a shade and/or optical effect produced by ESTA application cannot be copied pneumatically.
In order to prevent at least partly the shift in shade and change in optical effect, OEM finishes are refinished on the line at the automaker's plant using conventional basecoat materials, i.e., based on materials comprising organic solvents, whose shade and/or optical effect are adapted to those of the basecoats to be refinished. However, this approach is very complicated, since a conventional basecoat material has to be prepared and stocked at the automaker's plant separately for every production shade and/or effect.
European patent EP 0 521 040 B2 discloses a process for producing a multicoat refinish system in the conventional sense, in which a pigment-free, aqueous, film-forming coating composition is first applied in the region of the defect in the OEM finish, followed by an aqueous refinish basecoat material. The coating composition may be a pigment-free extract of the aqueous refinish basecoat material. A clearcoat material is then applied wet on wet to the aqueous basecoat film, after which the films present are cured together. This process constitutes a significant advance in refinish in the conventional sense.
The known refinish process, however, is unable to solve the above-mentioned problems which occur when multicoat color and/or effect paint systems are overcoated on the line at the automaker's plant, since said overcoating requires quite different amounts of coating materials and an entirely different logistical system than for refinish in the conventional sense, which of course is carried out above all in vehicle finishing workshops.
It is an object of the present invention to provide a novel process for overcoating multicoat color and/or effect paint systems, especially multicoat paint systems which have been produced by means of electrostatic spray application (ESTA) and curing and comprise at least one color and/or effect basecoat (A) produced from at least one aqueous basecoat material (A) and at least one clearcoat (B) produced from at least one liquid clearcoat material (B), said process no longer having the disadvantages of the prior art but instead giving multicoat color and/or effect paint systems, applied pneumatically wet on wet and cured, which suffer no deleterious shift in shade and/or no deleterious change in optical effect, especially metallic effect, as compared with the original or OEM finishes. Moreover, it is intended that the multicoat paint systems produced by means of the novel process should adhere very well to the OEM finishes. Not least, it is intended that the novel process should be suitable in particular for the overcoating of OEM finishes on the line at the automaker's plant, where the problems occurring are quite different to those associated with automotive refinish in the conventional sense.